The present invention relates generally to a magnetic random access memory (MRAM) device and a fabricating method thereof, and more particularly to a MRAM device write line structure
Magnetic random access memory (MRAM) technology development is currently underway for use as a type of non-volatile memory by the semiconductor industry. MRAM may also prove useful as dynamic random access memory (DRAM) or static random access memory (SRAM) replacements. There are two main types of MRAM: MTJ (magnetic tunnel junction) and GMR (giant magnetoresistive) MRAM. FIG. 1 shows a portion, or a memory bit, of an MTJ array 10 which includes a write line or a bit line 12 intersected by a number of digit lines 14. At each intersecting write line and digit line, a magnetic tunnel junction sandwich 16 forms a memory element in which one xe2x80x9cbitxe2x80x9d of information is stored. The magnetic tunnel junction sandwich 16 is comprised of a non-magnetic material 18 between a magnetic layer of fixed magnetization vector 20 and a magnetic layer in which the magnetization vector can be switched 22; these will be referred to as a fixed layer 20 and a free or switching layer 22.
It is advantageous for a variety of reasons to increase the packing density of memory cells in the memory array. A number of factors influence packing density; they include memory element size and the relative dimensions of associated memory cell circuitry, i.e. bit lines and digit lines, and any semiconductor switching or access device within the memory cell. For example, referring to FIG. 2, a cross-sectional view of a portion of a prior art MRAM write line structure 100 is shown. (The write line structure 100 can be a bit line structure in an MTJ array or a word line structure in a GMR array.) The write line structure 100 includes a conductive material 104 surrounded by magnetic cladding members 103 and 106. The magnetic cladding members 103 are formed using high-permeability materials that have magnet domains in the plane of the cross-section shown in FIG. 2 which are magnetized and demagnetized upon the application and removal of an applied magnetic field. When current is applied through the conductive material 104, the corresponding magnetic fields associated with the magnetic cladding members 103 and 106 help to enhance the magnitude and more effectively focus the overall magnetic field associated with the write line structure 100 toward its associated memory element (not shown). Additionally, the magnetic cladding members 103 and 106 also help to shield the bit line""s magnetic field from memory cells associated with other write lines, thereby protecting their programming state information.
The prior art method for forming the write line structure 100 includes first etching a trench 102 in the dielectric layer 101. Next, a layer of a high-permeability magnetic material, such as a layer of an alloy of nickel-iron (NiFe), is deposited over the dielectric layer 101 and in the trench 102. The layer of high-permeability magnetic material is then anisotropically etched to form magnetic cladding sidewall (spacer) members 103 adjacent the trench sidewalls. After forming the magnetic cladding sidewall members 103, a conductive material 104, such as copper or aluminum, is deposited overlying the dielectric layer 103 and within the trench opening 102. Then, portions of the conductive material 104 not contained within the opening 102 are removed using a chemical mechanical polishing (CMP) process. Finally, an overlying layer of high-permeability magnetic material is deposited, patterned, and etched to form the magnetic cladding capping member 106.
The magnitude of the magnetic field at the location of the memory element is enhanced by the presence of the cladding, thus less current is required in the conductive material 104. Because the magnetic cladding capping member 106 is formed overlying the trench 102, it must be patterned and etched having a width dimension Z which is yet greater than the trench 102 width dimension X. Moreover, alignment of the magnetic cladding capping member 106 to the trench 102 can be critical. Failure to properly align the magnetic cladding capping member 106 over the trench 102 can result in less-than-optimal magnetic fields being generated by the bit line or the undesirable exposure of adjacent circuitry to uncontained magnetic fields. Thus, the dimension Z of the magnetic cladding capping member 106 must additionally be upsized to take into account any alignment tolerance error. Therefore, an ability to reduce the dimension Z of the magnetic cladding capping member 106 can correspondingly improve the scalability of the MRAM array packing density.